The present invention relates, in general terms, to torsion-damping devices comprising at least two coaxial parts mounted rotatably relative to one another within the limits of a specific angular movement and against the action of elastic means designed to act circumferentially between them, referred to below for the sake of convenience as elastic means with circumferential action.
As is known, such a torsion-damping device is conventionally employed in a clutch plate assembly, especially for a motor vehicle, in which case one of its rotary parts comprises a friction disc intended to be fixed in rotation to a first shaft, in practice a drive shaft, for example the output shaft of the engine in the case of a motor vehicle, whilst another of the said rotary parts is carried by a hub intended to be fixed in rotation to a second shaft, in practice a driven shaft, for example the input shaft of a gearbox in the case of such a motor vehicle.
Such a torsion-damping device makes it possible to ensure controlled transmission of the torque applied to one of its rotary parts when the other is itself subjected to a torque, that is to say to filter the vibrations liable to arise over the entire length of the kinematic chain which extends from the engine to the controlled wheel shafts in the case of a motor vehicle.
The elastic means with circumferential action usually consist of springs of the helical-spring type which extend substantially tangentially to a circumference of the assembly and which, each individually, are arranged partly in a receptacle provided for this purpose in one of the rotary parts in question and partly in a receptacle likewise provided for this purpose in the other of the said rotary parts.
Also, more often than not, these elastic means with circumferential action are distributed in what is commonly called several "stages" which are of different rigidities and the intervention of which is adjusted as a function of the angular movement between the two rotary parts in question; only a first of these stages of relatively low rigidity intervenes at the start of this movement, and, in proportion to the development of the latter, one or more other stages of relatively higher rigidity subsequently add their own effects to those of the first.
In practice, for each of the springs of the stages of relatively high rigidity, the intervention of which is to be delayed in this way, a certain play is provided circumferentially for this purpose between the end edge of the receptacle, in which such a spring is located in one of the rotary parts in question, and the corresponding end edge of the receptacle in which it is located in the other of the said rotary parts.
In a given embodiment, this play is not necessarily the same for both directions of change in the angular movement between the rotary parts in question; it can, for example, be greater for that direction of change which corresponds to operation of the assembly in "traction", and is consequently less for that direction which corresponds to the operation of the latter "on the overrun".
Likewise, for a given total play, the relative values of this play for both of the directions of change in the angular movement are not necessarily the same for all the practical embodiments liable to arise.
The present invention is intended more particularly for the case where, in addition to the springs used in this way, the elastic means with circumferential action, interposed between the two rotary parts in question, incorporate at least one elastically deformable arm which, extending between two bearing elements, one designed to be fixed in rotation in a positive way to one of the said rotary parts and the other being provided with drive means designed to connect it in rotation to the other of the said rotary parts over at least one range of the angular movement between these, is cut out in one piece with the said bearing elements from a blank of small thickness.
Such an arrangement, which can advantageously make it possible to minimise the number of receptacles to be provided for springs in the two rotary parts in question, is described particularly in the French Patent filed on 3rd Nov. 1980 under No. 80/23,447 and published under No. 2,493,446, in which, in practice, the elastically deformable arm or arms used in this way constitute the first stage of relatively low rigidity of the corresponding elastic means circumferential action, instead of springs.
In this French Patent, pins or the like are provided more particularly for fixing one of the bearing elements of such an elastically deformable arm positively to one of the rotary parts in question.
Although such an arrangement is satisfactory, it has disadvantages, especially in that it is necessary to make perforations for installing such pins.
The subject of the present invention is, in general terms, an arrangement making it possible to avoid this disadvantage and resulting in other advantages.